深基坑一般采用（）的原则。
A、分层开挖，边撑边挖
B、分层开挖，先开挖后支撑
C、分层开挖，先撑后挖
D、不分层开挖，先撑后挖
参考答案：C
_______ in a poor family made Yuan Longping determined to solve the hunger problem in China when he was still young.
A．Bringing up
B．Being brought up
C．Having brought up
D．Brought up
板翅式换热器中隔板一般用（）材料制成。
A．铝锰合金
B．铅铝合金
C．铁铝合金
D．铝锌合金
